1. Field of the Invention
The present invention relates to an optical film having a superior anti-moisture characteristic and which efficiently changes the optical path of light having entered from a sidewise direction to a viewing direction and which enables formation of a slim, lightweight, bright, and easily-viewable liquid-crystal display device.
The present application is based on Japanese Patent Application No. 2000-25366, which is incorporated herein by reference.
2. Description of the Related Art
Demand exists for a slimmer and much lighter-weight reflection-type liquid-crystal display device for use in miniaturizing a portable personal computer or a cellular phone. Against this backdrop, a related-art reflection-type liquid-crystal device provided with a side-light-type light pipe and a front light involves use of a light pipe of 1 mm thickness or more required for realizing optical transmission. Hence, difficulty is encountered in miniaturizing the related-art liquid-crystal device of this type. Even in a case where a dual-purpose illumination-and-external-light liquid crystal display device with backlighting is embodied through use of a half-transmission type reflector, use of a sidelight light pipe is required. The thickness of the sidelight light pipe hinders miniaturization of the liquid-crystal device, as in the case of the sidelight-type liquid-crystal display device.
In the case of the liquid-crystal display device with backlighting using a half-transmission type reflector, addition of the half-transmission type reflector results in an increase in the weight of the liquid-crystal display device. As a result of light being separated into transmitted light and reflected light by means of the half-transmission type reflector, the view in an illumination mode becomes dark. Further, the view in an external-light mode also becomes dark. The brightness of the view falls short of the brightness of view obtained by a reflection layer of high reflectivity specifically designed for only reflection purpose.
The present invention is aimed at developing an optical film which efficiently changes the optical path of light having entered from a sidewise direction to a viewing direction and which enables formation of a slim, lightweight, bright, and easily-viewable liquid-crystal display device.
The present invention provides an optical film comprising:
a transparent film having an adhesive layer provided on one side thereof;
a layer which includes a plurality of groove structures, each structure having optical-path changing slopes oriented substantially toward certain directions at an angle of 35 to 48 degrees relative to the transparent film, and which is laid on the other side of the transparent film;
a transparent cover film for covering the surface of the layer in which the groove structures are formed; and
at least an anti-reflection layer and an anti-moisture layer laid on an exterior side of the cover film.
If the optical film according to the present invention is placed on a view surface of a liquid-crystal display panel having an illumination device disposed on the side thereof, the optical path of the light having entered from the side or the optical path of transmitted light of the incident light is efficiently changed to the viewing direction of the liquid-crystal display pane by way of the optical-path changing slopes formed in the optical film, thus effectively utilizing the light for liquid-crystal display. Thus, there can be formed a slim and lightweight liquid-crystal display device providing good display quality. By means of forming a smooth plane between the optical-path changing slopes, external light can be efficiently introduced into the liquid-crystal display panel. The incident light is subjected to reflection by way of a reflection layer, as is the light whose optical path has been changed. Thus, the incident light can be utilized for liquid-crystal display. In addition to an illumination mode, an external-light mode is also available on the liquid-crystal display panel. Consequently, there can be formed a slim, lightweight, and bright dual-purpose illumination-and-external-light liquid-crystal display device which provides superior display quality.
The above-described advantage is primarily ascribable to an optical film which controls an optical path by means of slope reflection. The light having entered from the side or transmitted incident light is subjected to reflection by way of the optical-path changing slopes, whereby the optical path of the light can be changed with superior directivity. Accordingly, good view can be achieved in an illumination mode. Further, a flat plane can be readily formed between the optical-path changing slopes. External light is caused to transmit through the flat lane, thus ensuring entrance of a sufficient amount of external light. Good view is achieved even in an external-light mode. Difficulty will be encountered in achieving such an advantage by means of a film of scattering and reflection type, such as a scattering sheet using rough surfaces. Unexamined Japanese Patent Publication No. Hei. 5- 158033 describes a reflection-type liquid-crystal display device, in which illumination light is caused to enter from the side surface of a liquid-crystal display panel, and the thus-entered light is subjected to total reflection by a view-side cell board. The thus-reflected light is subjected to scattering on a rough reflector, and the scattered light is utilized.
In this case, the light which can be utilized for display is light which is emanated from the panel after having been scattered and has not been subjected to total reflection. Scattered light usually exhibits a normal distribution showing a peak in the direction of regular reflection (the 20th Liquid-Crystal Forum Lecture Proceedings 3 G510, Tohoku University, UCHIDA Hitoshi). The display light is tilted sharply relative to the front direction (i.e., the vertical direction), and effective utilization of such light for display is difficult. Hence, dark display appears in the front direction. Even if the scattering characteristic of the rough reflector is made more intensive, the amount of light which is confined within the panel and cannot leave the panel is increased. Eventually, dark display occurs.
In contrast, the optical film according to the present inventionxe2x80x94which controls an optical path by means of slope reflectionxe2x80x94-primarily utilizes light appearing in the direction of regular reflection in which a peak appears, thus controlling an optical path of reflected light. Hence, directivity useful for display; particularly, directivity in the front direction, can be readily imparted to reflected light. Hence, bright display can be achieved even in a reflection mode. Further, the optical-path changing slopes are protected by a cover film, thus preventing groove structures from being clogged by soils. Soils can be readily removed by way of the soil-resistance layer, thus maintaining the optical-path changing function over a long period of time. Hence, the optical film can be utilized for a front-type liquid-crystal display device.